Method for cast calendering supercalendered coated paper



Feb 5, 1957 F. H. FROST ETAL 2,780,563

METHOD FOR CAST CALENDRING SUPERCALENDERED COATED PAPER ,Filed Dec.. 8, 1952 United States Patent METHOD FOR CAST CALENDERING SUPER- CALENDERED COATED PAPER Frederick H. Frost, Portland, and Robert E. Lane, Westbrook, Maine, assignors to S. D. Warren Company, Boston, Mass., a corporation of Massachusetts Application December 8, 1952, Serial No. 324,802

4 Claims. (Cl. 117-64) 4This invention relates to apparatus and processes for finishing or treating coated paper, coated on one or both sides, to produce thereon a Very high gloss, or a very level surface, or both. l

According to prior apparatus and processes for producing a high gloss and very level surface on coated paper, a paper web is coated with an aqueous suspension comprising pigments and hydrophilic swellable adhesives such as casein in the form of a Water soluble caseinate, and the coated paper is dried. The dried coating surface is then moistened with water or aqueous liquid. Immediately thereafter the moistened surface of the coating is pressed against a wet, heated, highly polished, smooth finishing surface against which Vit is kept in contact while i water is evaporated from the coating and the finishing surface, after which the coated paper is removed from the finishing surface. In one particular type of apparatus and method, a web of dried coated paper is carried by a press roll having a yielding surface and is pressed thereby against the wet surface of a heated, highly polished, smooth, chromium-plated, revolving finishing drum. The entering nip between the 4coated paper surface on the press roll and the finishing surface is supplied with aqueous liquid, so as to form a pool of such aqueous liquid in said nip. The surfaces of both the coating and the revolving drum passthrough and are wet by this pool of aqueous liquid in the nip. The wet surface of the coating is then immediately pressed by the press roll against the wet heated finishing surface with which it is kept in contact while moisture is being removed by evaporation.

We-have discovered that for reasons unknown to us, coated paper having a very high gloss or an exceptionally level coated surface, or both, can be produced at high speeds by the processes and/or apparatus of the present invention, whereas we have been unable to produce coated paper of equal quality at equal speeds, particularly in light weights, by any prior processes or apparatus known to us. p

Essentially, the 'present invention comprises premoistening the dried coated surface before it is passed through the pool of aqueous liquid in the finishing surface nip.

A particular apparatus suitable for carrying out the improved processes of the present invention comprises a cylindrical drum having a smooth, highly polished, chrome-plated, metal face, means for heating the drum, adjacent such drum a press roll having a yielding surface, for example, made of rubber, means for urging such press roll toward the drum surface lin pressing relation therewith, means for introducing aqueous liquid into the nip formed by the press roll and the drum, means spaced apart from but adjacent to the drum for applying aqueous liquid to a traveling coated web to pre-moisten the surface of the coating of such web before such web enters the above mentioned nip, such last mentioned means comprising a riding roll or a plurality of riding rolls in contact with the press roll and means for directing a fiow about 5 or 2,780,563 Fatented Feb. .5, 1957 of aqueous liquid onto the surface of such riding roll or rolls. Optionally one or more of the rolls, e. g. press roll, or riding roll or rolls, may be bored for circulation of liquid therethrough to control the temperature thereof.

It is undesirable to permit too long a time to elapse between the first application of aqueous liquid and the pressing of the surface of the coating against the wet finishing surface. In general, the coating surface should come into contact with the wet finishing surface within 6 seconds after it has been first moistened. However this is not essential in all cases. With the apparatus of the present invention, as described above, it is very easy to keep the elapsed time between the first wetting of the surface of the coating and the contacting of it with the wet finishing surface to less than 5 or 6 seconds. For example, if the paper travels 2 feet after the first application of moistening liquid and thereafter it reaches the wet finishing surface, even if the speed is as slow as ft. per minute the elapsed time will amount to only about 11A seconds. At higher speeds the elapsed time will be less.

At such higher speeds it is often desirable to move the station for the first-liquid application farther away from the finishing drum so as to obtain the desired lapse of time during which the coating is exposed to the first applied liquid.

This can be done by carrying out the premoistening step or first liquid application by means of a pair of rolls separate from the press roll.

The drawing illustrates one embodiment of the present invention.

Referring to the drawing, 1 is an unwinder which has wound thereabout a roll of dry, supercalendered coated paper 2, which is moved by press roll 3 having a yielding surface such as felt or rubber, through nip 11, formed by press roll 3 and finishing drum 7 having a chromium surface. The surface of press roll 3 is pressed or urged against the chromium surface of finishing drum 7 by known means such as a spring (not shown). Riding roll 4 rides on press roll 3, forming nip 10 through which the coated paper passes. A continuous stream of aqueous liquid is fiowed from an aqueous liquid source 5, onto the entire length of the surface of riding roll 4 to maintain the surface of riding roll 4 wet with aqueous liquid and therefore to maintain nip 10 wet. Another continuous stream of aqueous liquid is flowed from an- 'other aqueous liquid source 6 onto the entire length of by press roll 3. The chromium surface of drum 7 is heated by known means (not shown). The surface of the coating is removed from the revolving surface of drum 7 by means of take-off rollers 8 after it is substantially completely dried by the hot drum surface. The dried coated paper is thereafter rolled up on winder 9.

Preferably the rate of flow of liquid used for the premoistening step is smaller (usually 1A to 1/2) than the rate used forthe second wetting. However, the amounts of liquid which may be used in the pre-moistening step of the present invention are not limited to such quantities but depend primarily on the coating utilized. Preferably, the maximum rate of liquid flow against riding roll 4 should be controlled so that at the particular pressure exerted by riding roll 4 on press roll 3, the aqueous liquid will not spill out and overflow the ends of nip 10. However, rates of liquid flow against the surface of roll 4 may be utilized wherein slight overflow from the ends of nip 10 occur.

The aqueous liquid of the present invention may comprise water with or without additives such as ammonia,

3 surface active agents, metal wetting agents and/or formaldehyde;

Example A paper base stock whose furnish for each 1500 1b. beater included 10 lb. of rosin size (drybasis), enough alum to bring'the pH value to 5.5, 4() lbs. of clay and a small amount'of blue dyestuif had applied to it on one side only, 7 lbs. per ream (500 sheets 25 in. by 38 `in.), dry weight of an aqueous slurry containing (dry weight) 4000 lbs. clay, 1200 lbs. converted starch, dyestuff, fungicide, and enough water to make a solid content of 50.6% by weight. The resulting paper was calendered. The calendered paper was then coated on the other side with an aqueous slurry having a pH value of about 8.95 and consisting of `60'lbs.'clay, 40 lbs. calcium carbonate, 16 lbs, casein dissolved in alkaline casein solvent, small quantities of dyestuff and anti-foam agents, and enough water to make a solids content about 40% by weight. About 15.5 pounds of coating per ream, dry weight, was so applied. Thecoated paper was then driedand supercalendered, and the resulting paper was wound into a roll and taken to unwinder 1 shown in the drawing of the present application. Thereafter the web was fed over press' roll 3 with the last coated surface outward and was then fed downwardly through the nip 10 between riding roll 4 and press roll 3, thence downwardly through nip 11 between press roll 3 and heated drum 7, and around the drum. The coated paper was removed from the drum by take-off rolls 8 and wound up at Winder 9. An aqueous liquid was continuously fed by sprays to the entire length of the surface of the riding roll 4- from a liquid source 5 at the rate of about 1.2 gals. per 1000 sq. feet of coated surface. Such liquid had a pH of about 10.75 and consisted of water to which had been added in each gallon 0.084 lb. ammonia, 0.068 1b. formaldehyde and 0.007 lb. monoethanol ammonium stearate. Such liquid contained 0.09% solids. The same aqueous liquid was fed by sprays to the entire length of the surface of drum 7 from liquid source 6 at the rate of about 4.85 gals. per 1000 sq. feet of coated surface. From the drum `surface the aqueous liquid owed into nip 11 to form a pool in such nip. Efiiuent liquid flowed out of the ends of the nip 11 Vto the sewer in the amount of about 85 gallons per 100 gallons supplied to both the riding rolls and drum and contained 1.4% solids. The pH of the nip eiiuent was 10.5.y The surface lof the resulting coated paper had ahighly polished, very level finish.

While we are not sure, it is believed that in carrying out the preferred method of the present invention a thin filrn or layer of aqueous liquid isfonned on the surface of drum 7 as the coated paper passes through the nip 11 of the press roll surface and the drum surface. Hence it is believed that the moistened surface of the coating after passage through the nip pool is pressed against a thin film or layer of aqueous liquid on the drum surface and as the coated paper surface revolves with the hot drum surface, water from both said aqueous liquid and the mois'tened surface of the coating is evaporated and passes through the paper as vapor. The term wet,rhighly polished finishing surface as used in the claims includes a surface carrying a thin film or layer of the aqueous liquid supplied lto the nip 11.

Although it has been attempted to explain the theory of the present invention, it is not intended that the present invention be limited to such theory.

It should be understood that the present disclosure is for the purpose of illustration only and that the present invention includes all modifications and equivalents which fall Within the scope of the appended claims.

We claim:

1. A process for treating coated paper comprising applying aqueous liquid to thesurfacenof a layerof adty, superc'alendred, .hydrophilic coating carried by a paper web, said layer of coating cmprising a mineral pigment and an adhesive a substantial part of which is a hydrophilic swellable adhesive, to moisten at least the surface of said layer of coating, thereafter within not more than about 6 seconds passing said moistened surface through a pool of aqueous liquidf in Contact with aliighly polished finishing surface and'irn'mediately thereafter pressing said moistened surface against` said ,highly polished finishing surface, said aqueousl liquids beingLsubs'tanti'ally free of suspended solids.

2. A process for treating coated paper comprising applying aqueous liquid which is substantially free of suspended solids to the surface, of a layer of dry, supercalendered, hydrophilic (coating carried by a paper web, said layer of coating comprising a mineral pigment and an adhesivey a lsubstantial part of which is a hydrophilic swellable adhesive, pressingsaid moistened surface between two pressing members, thereafter within not more than about 6 seconds passing said moistened surface through a'pool of aqueous liquid substantially free of suspended solids and in contact with a highly polished finishing surface andimmediately thereafter pressing the moistened surface against said highly polished finishing surface.

3. A process for treating coatedpaper comprising applying aqueous liquid to the surface of a coated paper, the coating of said paper being dry, supercalendered and hydrophilic and comprising a mineral pigment and an adhesive ya substantial part of which is a hydrophilic swellable adhesive, by pressingthe same between two pressing members while directingI a flow of aqueous liquid against the surface` of the pressing member adjacent to the coated surface of the paper, to maintain the surface cf such member wet with said aqueous liquid, then within not vmore Vthan about 6 seconds passing the moistened surface through ai' pool of aqueous liquid in contact with a highly polished finishing surface and imniediatelyl thereafter pressing saidl moistened surface against said highiy-polishe'dfinishingsurface, said aqueous liquids being substantially free of suspended solids.

4. A process for treating coated paper comprising applying aqueous liquid tothe surface'of a coated paper, the coating of said paper being dry, supercalendered and hydrophilic and comprising a 'mineral pigment and an adhesive a substantial part of which is a hydrophilic swellable adhesive, by pressing the same against a roller surface which is wet with said liquid, thereafter within not more than about 6 seconds passing the moistened surface through a pool of' aqueous liquid in contact with a highly polished finishing surface and immediately thereafter pressing saidcoating surface against Vsaid highly polished finishing surface, said aqueous liquids being substantially free of suspended solids.

References Cited in thefile of this patent UNITED STATESPATENTS 2,003,065 Boyce May 28, 1935 2,006,209 Bradner June 25, 1935 2,069,786 Van der Meulen Feb. 9, 1937 2,088,893 Cates Aug. 3, 1937 2,293,278 Catesv Aug. 18, 1942 2,304,818 Gr'upe Dee. l5, 1942 2,304,819 Grupe(` Dec. 15, 1942 2,611,717 Sooy Sept. 23, 1952 2,617,743 Grimm Nov 11, 1952 2,678,890 Leighton M ay 18, 1954 

1. A PROCESS FOR TREATING COATED PAPER COMPRISING APPLYING AQUEOUS LIQUID TO THE SURFACE OF A LAYER OF A DRY, SUPERCALENDERED, HYDROPHILIC COATING CARRIED BY A PAPER WEB, SAID LAYER OF COATING COMPRISING A MINERAL PIGMENT AND AN ADHESIVE A SUBSTANTIAL PART OF WHICH IS A HYDROPHILIC SWELLABLE ADHESIVE, TO MOISTEN AT LEAST THE SURFACE OF SAID LAYER OF COATING, THEREAFTER WITHIN NOT MORE THAN ABOUT 6 SECONDS PASSING SAID MOISTENED SURFACE THROUGH A POOL OF AQUEOUS LIQUID IN CONTACT WITH A HIGHLY POLISHED FINISHING SURFACE AND IMMEDIATELY THEREAFTER PRESSING SAID MOISTENED SURFACE AGAINST SAID HIGHLY POLISHED FINISHING SURFACE, SAID AQUEOUS LIQUIDS BEING SUBSTANTIALLY FREE OF SUSPENDED SOLIDS. 